1. Field of the Invention
This invention relates to adducts of phosphinic acid with maleic acid semiesters, to a process for their production and to their use as flotation aids.
2. Description of Related Art
There are many known processes for the concentration of valuable non-sulfidic (i.e. sulfide free) minerals from size-reduced crude ores by flotation. Examples of these valuable minerals include apatite, fluorite, scheelite and other salt-like minerals, cassiterite and other heavy-metal oxides, for example those of titanium and zirconium, and also certain silicates and alumosilicates which are floated in the presence of collectors. According to "Ullmanns Enzyklopadie der technischen Chemie", Verlag Chemie, Weinheim (1972), Vol. 2, page 115, collectors are organic compounds which generally carry one chemically active polar group on a more or less long hydrocarbon chain. Fatty acids, particularly unsaturated fatty acids, preferably oleic acid, are frequently used as collectors. Other suitable collectors are, for example, sulfonate surfactants (such as alkylaryl sulfonates) or alkyl or aryl phosphonates.
Sulfosuccinic acid monoalkyl esters and sulfosuccinic acid aspartates are proposed as collectors in U.S. Pat. Nos. 4,138,350 and 4,139,482. However, collectors such as these, which are based on fatty acids or sulfonates, are comparatively non-selective because they also float silicate- and carbonate-containing minerals and accordingly can only be used to a limited extent if such minerals accompany other valuable minerals and are to be separated therefrom. Accordingly, other aids, for example so-called "depressors", have to be added to prevent the flotation of unwanted gangues. The resulting mixtures of reagents for flotation have a very complex composition. The selective flotation of valuable non-sulfidic minerals in the presence of calcite as gangue represents a particular technical problem for which fatty acids and collectors containing sulfo groups are not sufficiently suitable in practice.
U.S. Pat. No. 4,430,238 describes dicarboxylic acid semiesters esterified with acylated alkylene oxides, for example maleic acid semiesters esterified with fatty acid acylated alkylene oxides and their use as collectors for the flotation of oxide or salt-like minerals. However, the disadvantage of these compounds is that they are also not sufficiently selective in practice and accordingly necessitate the additional use of other modifying reagents.